Janek and Wanda live in a small room in a villa, while other rooms are occupied by offices of various institutions. Janek often stays at work after hours, just to avoid returning to the cramped apartment too early. One day, a man named Malinowski, who once lived in the same small room, visits the couple. He proposes to exchange their room for a new, two-room apartment that he has just received. Janek and Wanda are initially distrustful, but eventually, the exchange takes place. It turns out that Wanda's ex-husband, Jerzy, already lives in the new apartment. Despite the divorce, as he is registered with Wanda, he has the right to continue living in her apartment. Janek tries to find a way to get rid of the intruder.
Jerzy Szajnowicz-Ivanov, the son of a Polish mother and a Russian father, raised in Greece, reports to the Carpathian Brigade in the spring of 1941. While the Poles are wary of him at first, he proves his worth by taking part in several sabotage actions against the Nazis.